Directed Evolution Under Pressure

A research team demonstrated the adaptability and survival of the model bacterium Escherichia coli to hydrostatic pressures of 2 GPa.

MicrobesThe adaptability and survival of the model bacterium Escherichia coli to hydrostatic pressures of 2 GPa were demonstrated recently by a research team working jointly at Katholieke Universiteit Leuven (Department of Microbial and Molecular Systems) and University College London (Department of Chemistry). The work suggests that life could penetrate to greater depths inside planets than previously imagined, on Earth or elsewhere.

A paper [1] describing the work was published in January 2011 in the new online journal mBio. Previous research reported in 2002 demonstrated the viability of E. coli at gigapascal pressures [2].  The recent experiments, which were started by the Leuven microbiology group, focused on directed evolution and the potential of E. coli to develop resistance against even higher pressures. After each progressively higher-pressure exposure, surviving bacteria were allowed to recover and grow at ambient conditions, in order for spontaneous mutants with increased resistance to automatically enrich the population.

After resistance surpassed 700 MPa, the researchers moved to London to continue directed evolution at higher pressures made possible by a newly designed high-pressure cell. This cell, combined with piston cylinder techniques, enabled experiments up to and beyond 2 GPa. It was ultimately shown that E. coli mutants could be isolated that resisted pressures up to 2 GPa, while no survivors from the original wild type bacterium could be found above 700 MPa. Aside from the extreme resistance itself, the relative ease of acquiring this trait proved almost equally remarkable. In fact, GPa-resistant E. coli mutants reproducibly evolved after a limited number of generations and suffered no apparent loss of fitness at atmospheric conditions. Thus, resistance can develop on a very short evolutionary time scale. The researchers also found no evidence for a cross correlation between the acquisition of high pressure versus high temperature tolerance.

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